I recently travelled to southern British Columbia, Canada. I visited the Vancouver area as well as areas hundreds of miles to the east in the mountains. While there, I noticed that high voltage transmission lines (or, as they called there, "hydro lines") do not have ground conductors.
Everywhere else I have been, transmission lines usually have one or two sets of three phases hanging on insulators plus an additional one or two lines attached directly to the tower structure usually at the highest point. I always assumed they were for lightning protection. Wikipedia seems to support that. Anyone know why are they not needed in BC?
You have a cite for that? From what I can see, looks like they have some very limited installations where it's being tested out and talk, but I don't see anything that indicates power companies are sold on it, rapidly deploying it. I'm not even sure what the exact point is. Guessing it's reduced losses from skin effect?
And what's the relevance in terms of the question?
Typically here I see the smaller wires strung along the tops of distribution towers like Pat says. Whether they are there just for lightning protection or if they are an essential part of the system, IDK. If it's 3 phase, balanced, then no current would flow in them anyway.
I know it's not much, but those transmission conductors are big, probably 1 1/4"+, so skin effect could have some economic effect on the equation. And if it's not that, then IDK what the advantage to going to DC is supposed to be? I can think of some big drawbacks, like having to convert from AC to DC, then DC to AC again at those huge power levels.
"HVDC requires less conductor per unit distance than an AC line, as there i s no need to support three phases and there is no skin effect."
"It is because HVDC typically comprises active power flow only and thus cau ses lower losses than HVAC lines, which comprise active and reactive power flow."
"The disadvantages of HVDC are in conversion, switching, control, availabil ity and maintenance.
HVDC is less reliable and has lower availability than alternating current ( AC) systems, mainly due to the extra conversion equipment. Single-pole syst ems have availability of about 98.5%, with about a third of the downtime un scheduled due to faults. Fault-tolerant bipole systems provide high availab ility for 50% of the link capacity, but availability of the full capacity i s about 97% to 98%.[22]
The required converter stations are expensive and have limited overload cap acity. At smaller transmission distances, the losses in the converter stati ons may be bigger than in an AC transmission line for the same distance. Th e cost of the converters may not be offset by reductions in line constructi on cost and lower line loss."
Kind of what I thought, it's not exactly without issues of it's own. One thing there that makes no sense is the part about it not requiring
3 phases. That's true, but so what? All those 3 phase conductors are transferring power, just like all the conductors in a DC system would. The reactive power part, I hadn't thought about, but that would be a big thing, depending on how much power typically is reactive on a power transmission line. You would think they would do everything they can to get it close to zero.
You are right, those are for lightning protection but I am not sure why they think they do not need them. This was in Montana, not that far south and they used a "static line" there.
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(BTW it is just an optical illusion that these are on the ground)
One point made elsewhere in the article is that when DC is used to interconnect 2 AC systems, they do not require synchronization of the phases, or the frequency (50 vs 60 Hz).
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Also, DC lends itself to underwater/underground HV cabling, where AC does not.
Is there a valley to the left of the nearest toweer?
The local REAs have been using smaller wires and installing them in twisted pairs. I'm guessing the twisted pairs shed ice more readily than a single, larger conductor. They also put what looks like a twisted rod in the middle of some wire spans. Again, my guess is for ice/wind.
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